Photoconductive compositions and elements containing methine dye in j-aggregate state

ABSTRACT

Organic photoconductive compositions containing a methine dye present in the J-aggregated state and which spectrally respond primarily in the J-band are described. The resultant compositions can be used as photoconductors or as sensitizers for other photoconductors.

United States Patent 1191 Gilman et a1.

[451 Oct.30,19 73 PHOTOCONDUCTIVE COMPOSITIONS AND ELEMENTS CONTAININGMETHINE DYE IN J-AGGREGATE STATE [75] Inventors: Paul B. Gilman; DonaldW.

I-Ieseltine, both of Rochester, N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

[221 Filed: Jan. 26, 1972 [21] Appl. N0.: 221,037

Related US. Application Data [63] Continuation-in-part of Ser. No.804,267, March 4,

1969, abandoned.

[52] US. Cl 96/l.6, 96/130, 96/129 [51] Int. Cl G03g 5/06 [58] Field ofSearch 96/130, 132, 1.5, 96/l.6

[56] References Cited UNITED STATES PATENTS 3,469,987 9/1969 Owens eta1. 96/102 3,676,147 7/1972 Boyer et al. 96/130 OTHER PUBLICATIONSRosenoff et al., The Resolved Spectra of Small Cyanine Dye Aggregatesand a Mechanism of Supersensitization, Photo. Science & Eng, Vol. 12,N0. 4, 185-195, July, 1968.

Primary ExaminerGeorge F. Lesmes Assistant Examiner-M. B. Wittenberg vAttorney-Robert W. Hampton et a1.

[57] ABSTRACT ductors.

17 Claims, No Drawings PHOTOCONDUCTIVE COMPOSITIONS AND ELEMENTSCONTAINING METHINE DYE IN J-AGGREGATE STATE This application is acontinuation-in-part of our application Ser. No. 804,267 filed Mar. 4,1969 now abandoned.

This invention relates to electrophotography, and more particularly, tophotoconductive compositions and sensitizers for photoconductivecompositions.

Electrophotographic imaging processes and techniques have beenextensively described in both the pa-' tent and other literature, forexample, U.S. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809;2,551,582; 2,825,814; 2,833,648; 3,220,324; 3,220,831; 3,220,833 andmany others. Generally, these processes have in common the steps ofemploying a normally insulating photoconductive element which isprepared to respond to imagewise exposure with electromagnetic radiationby forming a latent electrostatic charge image. A variety of subsequentoperations, now well known in the art, can then be employed to produce apermanent record of the image.

One type of photoconductive insulating structural element particularlyuseful in electrophotography utilizes a composition containing aphotoconductive insulating material dispersed in a resinous material.- Aunitary electrophotographic element is generally produced in amulti-layer type of structure'by coating a layer of the photoconductivecomposition onto a film support previously overcoated with a layer ofconducting material or else the photoconductive composition can becoated directly onto a coating support of metal or other suitableconducting material. Such photoconductive compositions show improvedspeed and/or spectral response, as well as other desiredelectrophotographic characteristics, when one or more photosensitizingmaterials or addenda are incorporated into the photoconductivecompositions. Typical addenda of this latter type are disclosed in U.S.Pat. Nos. 3,250,615; 3,141,770; and 2,987,395. Generallyphotosensitizing addenda used in photoconductive compositions areincorporatedto effect a change in the sensitivity min the speed of aparticular photoconductor system and/or a change in its spectralresponse characteristics. Such addenda can enhance the sensitivity of anelement to radiation at a particularwavelength or to a braod range ofwavelengths where desired. The mechanism of such sensitization ispresently not fully understood. The phenomenon, however, is extremelyuseful. The importance of such effects is evidenced by the extensivesearch currently conducted by' workers in the art for compositions andcompounds which are capable of photosensitizing photoconductivecompositions in the manner described.

Usually the desirability of a change in electrophotographic propertiesis dictated by the end use contemplated for the photoconductive element.For example, in document copying applications the spectral sensitivityof the electrophotographic response of the photoconductor should becapable of reproducing the wide range of colors which are normallyencountered in such use. If the response of the photoconductor fallshort of these design criteria, it is highly desirable if the spectralresponse of the composition can be altered by the addition of spectralsensitizing addenda to the composition. Likewise, various applicationsspecifically require other characteristics such as high extrictioncoeffiaggregate are used for forming heterogeneous compo- 'cients and animproved mechanism of charge conduction. It is also desirable for thephotoconductive element to exhibit high shoulder speed and high toespeed as measured in an electrical characteristic curve (charge v.exposure).

Spectral sensitization of many photoconductive compositions by theaddition of certain dyes selected from the large number of dyespresently known has hitherto been widely used to provide for the desiredflexibility in the design of photoconductive elements in particularphotoconductor-containing systems. At. the present time, however, fewsensitizing addenda to photoconductor compositions or elements have beenshown to the art which are capable of producing a significantimprovement in, substantially all of the aforementioned desirablecharacteristics. Conventional dye addenda to photoconductor compositionshave generally shown only a limited capability for over-all improvementin the totality of electrophotographic properties which cooperate toproduce a useful electrophotographic element or structure. The art isstill searching for improveme'nts in effective spectral sensitizers forphotoconductive compositions: Thus far, conventional dye sensitizationalone has not produced the quality of improvement inphotoconductor-containing systems which might be considered satisfactoryfor the wide varietyof electrophotographic applications presentlycontemplated by workers in the art.

It is, therefore, an object of this invention to porvide the art ofelectrophotography with novel compositions of matter, method for theirpreparation and elements for their optimum employment.

It is a further object of this invention to provide novel means forspectrally sensitizing photoconductive compositions and elements for theemployment of such sensitized compositions.

It is also an object of this invention to provide nove photoconductivecompositions having high extinction coefficients.

i It is still another object to provide novel photoconductivecompositions having higher speeds.

The above and further objects and advantages of this invention willbecome apparent from the following description of the invention. I

We have discovered that spectral sensitization of photoconductivecompositions containing an electrically insulating polymer as a bindercan be obtained by the formation of J-aggregate's of certain methinedyes in the photoconductive compositions to form a twophase orparticulate-containing composition. In addition, we have'found a varietyof novel means for obtaining a high percentage of such aggregated dye inphotoconductive compositions.

The dyes useful in accordance with this invention can be generallycharacterized as methine spectral sensitizing dyes which have shown theability under variouscircumstances to form J-type aggregates. Thischaracteristic present in certain dyes is extensively discussed in C. E.K. Mees, The Theory of the Photographic Process, 3rd edition, pp. 215,234, 240, 245, 248 and 254 and MG. deW. Anderson, Stereochemical FactorsAffecting Optical Sensitization, Proceedings of the InternationalConference on Scientific Photography at Liege, 1959, pp. 487 ff. Dyesexhibiting the ability to J- sitions of this invention when combinedwith a photoconductive electrically insulating composition in accordancewith this invention. When the useful dyes are aggregated and contiguouswith a photoconductor in accordance with the novel methods of thisinvention, not only is the spectral sensitivity ofthe photoconductorincreased but in addition the new photoconductive composition appears tohave a better mechanism of charge conduction. This latter added featureis probably the result of the ordering of the molecules when in thisaggregated state. I

The spectral sensitizers used in accordance with this invention aremethine dyes, including polymethine dyes, characterized by their abilityto form J- aggregates. Methine dyes are dyes containing at least onemethine group, including substituted methine groups, as part of achromophore group in the dye. Methine groups can be represented by theformula wherein n is an integer having a value of O, l, 2 or 3 and Q isa hydrogen atom, a lower alkyl group (e.g., one to six carbons) or anaryl group such as phenyl. Particularly useful methine dyes include.l-aggregating cyanine dyes. The term cyanine dye as used herein, is tobe construed broadly as inclusive of simple cyanines, carbocyanines,including polycarbocyanines such as dicarbocyanines, tricarbocyanines,etc. The term includes symmetrical as well as unsymmetrical dyes, aswell as chain-methine substituted dyes. Cyanine dyes useful hereinfeature the amidinium ion chromophoric system. See Mees and James, TheTheory of the Photographic Process" published by MacMillan Company(1966) page 201 et seq. The term cyanine dye is also meant to includethe following dyes: 2,2'-cyanines and carboxyanines, thiacyanines,oxacyanines, thia-2'- cyanines, N,N-cthylene bridged thiacyanines, 9-substituted thiacarbocyanines, naphthothiazolocyanines,naphthoxazolocyanines, allopolar cyanines, complex cyanines(rhodacyanines), bridged cyanines, and the like. Also included under theterm cyanine are thosedyes featuring the amidinium-ion chromophoricsystem but which have only one nitrogen atom in a heterocyclic ringthrough which a portion of the conjugated chain passes, such as'hemicyanine dyes. Preferred aggregating cyanine dyes useful in theinvention can be represented by the formula:

wherein Z'is an acid anion; Q is a hydrogen atom, a lower alkyl radical(e.g., one to six carbon atoms) or an aryl radical such as phenyl; n isan integer having a value of 0, l, 2 or 3; and X and Y are the atomsnecessary to complete a heterocyclic nucleus having five to six atoms inthe hetero ring such as benzothiazole, benzoxazole, benzimidazole, etc.Styryl dyes, for example, alkylaminostyryl dyes and merocyanine dyes arealso useful. The term merocyanine is also used broadly and includes dyeswhich are characterized by the amidic chromophoric system. See Mees andJames,

supra, pages 201 and 21 8.

Representative examples of dyes useful in the invention includecompounds listed in Table I.

TABLE 1 Compound Name of No. Compound 13,3'-diethyl-5,5'-dimethyl-9-ethyl thiacarbocyanine chloride 2anhydro-S,5,6,6'-tetrachloro-l ,l ,3-triethyl-3-(3-sulfobutyl)benzimidazolocarbocyanine hydroxide 3 anhydrol -ethyl-l4-sulfobutyl )-2,2

cyanine hydroxide 4 3,3'-dimethyl9-phenyl-4,5,4',5'-dibenzothiacarbocyanine bromide 5 anhydro-5,5',6,6'-tetrachlorol l -diethyl- 3,3'-di-(3-sulfobutyl)benzimidazolocanbocyanine hydroxide 6 5,5-dichlorol ,1',3,3'-tetramethylbenzimidazolocarbocyanine perchlorate 7l',3-diethylthia-2'-cyanine chloride 83,3,9-triethylselenathiacarbocyanine perchlorate 9 3 ,3 '-dimethyl-8, lO-diphenoxyoxacarbocyanine chloride 102-(5,5-dicyano-2,A-pentenylidene)3-ethylbenzothiazoline l l3,3'diethyl-9-rnethylthiacarbocyanine chloride 12l-ethyl-3-methylthia-2'-cyanine chloride 13l,l'-diethyl-6,6-dimethyl-2,2' -cyanine perchlorate l4anhydro-3,9-diethyl-3-sulfobutyl-5,5'-

diphenyloxacarbocyanine hydroxide l53,3'-triethyl-5,5'-dichlorothiacarbocyanine bromide l63,3'-dimethyl-Q-ethylthiacarbocyanine bromide 17 3 ,3"diethyl-9-methyl-4,5 ,4',5 '-dibenzothiacarbocyanine bromide l8 3 ,3'-dimethyl-9-phenyl-4,5 ,4',5 '-dibenzothiacarbocyanine bromide l9l,l'-diethyl-2,2-cyanine chloride 203'-ethyl-l-methyl-5,6-dinitro-2-phenyl-3- indolothiacarbocyaninep-toluenesulfonate 21 2 2-[2-(4-bromophenyl)-6- methoxyimidazo[ l,2-b]-pyrida zin-3- yl]vinyl}-3-ethyl-6-nitrobenzothiazoliump-toluenesulfonate 22 anhydro-2-[2-(3,5-dimethyl-l-p-sulfophenyl-4-pyrazolyl)vinyl]-3-ethylthiazolo[4,5 blquinovlinium hydroxide 233'-ethyl-l-methyl-5,6'-dinitro-2-phenyl-3- indolthiacarbocyaninep-toluenesulfonate 24 l,3,3,3 -tetramethyl-5,6'-dinitroindothiacyaninep-toluenesulfonate 25 2-[(3,5-dimethyl-l-phenyl-4-pyrazoly)vinyl1-3-ethylthiazolo[4,5-b]quinolinium chloride 263,3',9-triethyl-5,5-diphenyloxacarbocyanine bromide 27 3,3'-diethyl-9-methylthiacarbocyanine p-toluenesulfonate 28anhydro-tS-chloroQ-l2-(3,5-dimethyl-1-psulfophenyl-4-pyrazolyl )vinyl l,3-

diphenyl-imidazo[4,5-b]qunioxalinium hydroxide 296,7-dichlor0-1,3,3'-trimethyl-l,3-diphenylimidazo[4,5-b]quinoxalinoindocarbocyanineiqditlq. 30 3'-ethyll -methyl-5;6'-dini!ro-2-phenyl-3-indolothiacarbocyanine p-toluenesulfonate 3l 2-[(3,5dimethyll -phenyl-4-pyrazolyl)vinyl l ,3 ,3-trimethyl-3 H- pyrrolo[2,3-b]pyridinium iodide32 l,3-diallyl-3-methyl-6'-nitroimidazo[4,5-b1- quinoxalinothiacyaninep-toluenesulfonate 33 3-ethyl-6-nitro-2-l 2-( l-phenyl-4-pyrazolylvinyllbenzothiazolium p-toluenesulfonate 342{2-[l-(2-benzothiazolyl)-3,5-dimethyl-4-pyrazolyl]vinyl}-3-ethyI-6-nitr0benzothiazolium p-toluenesulfonate 35l,3-diallyl-2-[ 2-( l-phenyl-4-pyrazolyl)vinylimidazo[4,5-b1quinoxalinium p-toluehesulfonate 36 anhydro-2-[2-( 3,S-dimethyll -p-sulfophenyl-4-pyrazolyl)vinyl]-3-ethylthiazolo[4,5-blquinolinium hydroxide 376,7-dichloro-2-[2-( l-methyl-2-phenyl-3- indolyl )vinyl l,3,-diphenylirnidazo[4,5- b]-quinoxalinium p-toluenesulfonate 38l,3-diallyl-l '-methyl-5 '-nitro-2'- phenylimidazo[4,5-b]quinoxalino-3indolocarbocyanine p-toluenesulfonate 3'-ethyll.3.3-trimethyl-5.6-dinitroindo thiacarbocyanine p-toluenesulfonate5-chloro-2[2-( 3 ,5 -dimethyll -phenyl-4- pyrazolyl )vinyl ]-l ,3,3-trimethyl-3H- indolium iodide l, l ,3 ,3-tetraethylimidazo['4,5-

b]quinoxalinocarbocyanine chloride 3-[ (6,7-dichloro-l ,3-diphenyll H-imidazo[4,5-b]-quinoxalin-2(3H)- ylidene)ethylidene]-2 H-pyrido[ l,2-a]pyrimidine-2,4(3H)-dione 5 .5 '-dichloro-3,3."-diethyl-6,6'-dinitrothiacarbocyanine iodide 3-ethyl-6-nitro-2-[ 2-(l ,3 ,5-triphenyl-4- pyrazolyl)vinyllbenzothiazolium iodide2-{2-[2-(4-bromophenyl)-6- methoxyimidazo-[ l,2-b]pyridazin-3yllvinyl}-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate We havefound 'means for preparing sensitized photoconductive compositionscontaining a methine dye which spectrally responds predominantly in theregion of J-aggregation. We have found 'that the dye need not all beJ-aggregated. It is not always necessary to have the dyes completelyaggregated as long as so much is tion appear to be comprised only ofdye. The present J -aggregated dyes alone as carried in a suitablepolymer matrix'have photoconductive properties as well as sensitizingproperties for other photoconductors.

One method for forming the present organic photoconductive compositionssensitized with J-aggregated dye that is particularly useful involvesaggregating basic dyes. According to this method, the basic dyes areprotonated prior to their incorporation into a photoconductivecomposition. The particular method for protonating the dye can beselected from any of a wide variety of well-known protonationtechniques. One suitable technique is the addition of p-toluene-sulfonicacid to the basic dye. Another equally suitable technique is to fume abasic dye solution with hydrogen chloride. Generally, protonation willcause the dye to become colorless. The protonated dye which is not yetin the J-aggregated state is then much more soluble in the organicsolvents used in preparing a photoconductive coating and thus can bemore easily mixed into the photoconductive composition. At this point,the dye is generally still not in the aggregated state; however, avariety of procedures can be followed subsequently to convert the dye toits colored state after mixing: into the photoconductive composition andto cause it to be converted to the J-aggregate. Fuming thedye-containing photoconductive composition with ammonia is aparticularly useful'method for neutralizing the protonated dye while itis in a polymeric matrix of a photoconduc- 0 tive composition.Neutralization thus results in the foraggregated that the dye-containingcomposition spec- I trally responds primarily in the so-called .l-band.In general, a predominant portion of the dye is present in the.l-aggregated state and preferably substantially all of the dye presentis in the .l-aggregated state.

The exact mechanism involved in the formation of the J-aggregatc is notentirely known. However, the presence of the aggregate is readilydetermined by the characteristic intense, narrow absorption band (J-band) seen at a longer wavelength than the typical absorption band forthe non-aggregated form of a dye. It has been suggested that the .l-bandarises from interaction of dye molecules in a large aggregate of the dyeeither as a nematic crystal, or on a polymer matrix or micellarstructure. The basic mechanism is presently not wholly defined; however,as referred to above, the J- band per se is readily observed and hasbeen well known since the original workof Dr. E. E. Jelley for whom thisband is named.

The J-aggregates formed in accordance with this invention not onlyproduce an observable longwavelength absorption band, but' in additionthe J- aggregates, are often visible whenobserved microscopically. Theaggregates, which give a heterogeneous nature to the photoconductivecompositions sensitized therewith, generally have a particle size offrom about 2 X 10' to about 1 X 10" mm. with a preferred range aggregateparticles prepared according to this invenmation of a J-aggregated stateof the dye. Such secondary neutralization procedures are sometimes notnecessary if the photoconductive composition itself is sufficientlybasic in relation to the dye; In this latter situation, mer'e mixing ofthe protonated dye with the basic photoconductive composition will causeformation in situ of the desired .I-aggregated state of the dye.

v A further method of forming the present J -aggregate s is to mix theaggregating dye or dyes into a photoconductive composition, coat a layerof the material and then subject it to the-fumes of various solvents.Particular ly useful solvents include chlorinated hydrocarbon solventssuch as methylene chloride, ethylene chloride, etc. .Also useful arearomatic hydrocarbon -solvents such as benzene, toluene, 'etc.

Another suitable method for theformation of the sensitizedphotoconductive compositions according to this invention involvesrnetachromism. Metachromism as referred to here is the use of amaterial, such as an organic polymer with dyesin solution in orderto'change the state of the'dye from the non-aggregate to the J'-(longwavelength) aggregate form. A metachromic interaction can be readilyobserved by a shift in the absorption spectrum of the-dye used. A usefulmetachromatic method for converting a dye to the described aggregateform involves the cooperation of a charged form of an aggregating dyewith an oppositely charged material, such as a charged polymer. Thecharged dye is thoroughly mixed into a photoconductive compositioncomprising a polymeric binder'having aphotoconductor dispersedor'dissolved therein. Thereafter, a, solution of an oppositely chargedmaterial is prepared, such as a solution of a cationic polymer. Thecationic polymer and the dye-containingphotoconductive com-- positionare then mixed together to form the J- aggregate form of the dye.Alternatively, a cationic polymer solution can be coated on a supportand the dye-containing photoconductive composition coated thereover. Ineither situation after contacting the anionic dye species with thecationic polymeric material, the formation of the J-aggregated form ofthe dye is en- .hanced. Although the exact mechanismof this system isnot fully understood, the anionic-cationic relationship between thecharged dye and the charged polymeric material facilitates the formationof the J- aggregated state of the dye. In addition to the aboveprocedure, a similar procedure can be followed using a cationic speciesof dye and using an anionic material, such as a charged polymer, tofacilitate the formation of the J-aggregate. A wide variety of chargedorganic polymers can be used to induce the present metachromicinteraction. Materials useful in the practice of this method includepoly(vinylbenzyltrimethylammonium chloride), 2,7-naphthalenedisulfonicacid, the sodium salt of naphthalenesulfonates, etc. A variety ofantistatic materials have proved useful such as Napcostat which is awater-soluble low volatility cationic material produced by condensingvarious aromatic hydroxy compounds with 9 to 19 moles of ethylene oxideper hydroxy radical as disclosed in U.S. Pat. No. 3,333,983 and made byNapco Chemical Co. Other useful materials are Compound 79OL which is anantistatic agent made by Merix Chemical Co. and Mollisan which is anonionic material manufactured by Onyx Chemical Co.

Still another means for forming the aggregated dye in a photoconductivecomposition involves the use of high moisture conditions during thecoating operation. This method can be accomplished in several ways. Oneuseful way involves forming a coating dope of the photoconductor, binderand sensitizing dye and coating the dope on a support in contact with acold coating block so as to cause condensation of moisture on thecoating surface. Alternatively, the dope can be coated in the usualmanner only in the presence of steam. It is also possible to produce theaggregated dye by forming a coating of this dope and then subjecting itto steam at a later time.

A further suitable technique for forming the described aggregatesinvolves dissolving a J-aggregating dye in alcohol and very thoroughlymixing the dyealcohol solution into a typical photoconductivecomposition. A very satisfactory method for obtaining the requisitethorough mixing is through the use of an ultrasonic mixing devicealthough other methods could be used. Useful alcohols include loweralkanols such as those having from one to three carbon atoms such asmethanol, ethanol, propanol, etc., with methanol giving the bestresults. Although the exact reasons that make this method useful are notknown, it is believed to be partly due to the solubility of the dyes inalcohol. This solubility gives rise to increased dispersion in solutionwhich makes it possible to disperse the dye more readily and thoroughlythroughout the polymer matrix of the photoconductive composition.

Any of the above techniques for forming the J- aggregated dye in aphotoconductive composition can also be used to form the J-aggregate ina polymeric binder which does not contain a photoconductor. Theaggregate-containing polymeric material can then be used to sensitize atypical photoconductive composition in a variety of ways by bringing theaggregate and photoconductor into contiguous relationship such as bycoating the photoconductive composition over a layer of theaggregate-containing binder. Sensitization can also be accomplished byovercoating a photoconductive composition with an aggregate-containingpolymeric material. If so desired, sensitization can likewise beaccomplished by mixing an aggregate-containing polymeric material into aphotoconductive composition.

In accordance with this invention, photoconductive compositions can besensitized with more than one J- aggregating dye. If two dyes are usedwhich have J- bands at slightly displaced regions of the spectrum, thetwo will produce a combined result. By using various combinations ofdyes, it is possible to prepare sensitized photoconductive compositionshaving peak sensitivity at different wavelengths than would be possibleusing only one dye.

The present invention can readily be used for enhancing the sensitivityand extending the spectral range of sensitivity of a variety of organicphotoconductors including both nand p-type photoconductors. For example,the present invention can be used in connection with organicphotoconducting materials which have little or substantially nopersistence of photoconductivity. An especially useful class of organicphotoconductors is referred to herein as organic amine photoconductors.Such organic photoconductors have as a common structural feature at leasone amino group. Useful organic photoconductors which can be spectrallysensitized in accordance with this invention include, therefore,arylamine compounds comprising (1) diarylamines such as diphenylamine,dinaphthylamine, N,N-

diphenylbenzidine, N-phenyl- 1 -naphthylamine N-phenyl-2-naphthylamine,N,N'-diphenyl-pphenylenediamine, 2-carboxy-5-chloro-4methoxydiphenylamine, p-anilinophenol, N,N'-di-2-naphthyLp-phenylenediamine, those described in Fox U.S. Pat. No.3,240,597, issued Mar. 15, 1966, and the like, and (2) triarylaminesincluding (a) nonpolymeric triarylamines, such as triphenylamine,N,N,N',N'-

tetraphenyl-m-phenylenediamine 4- acetyltriphenylamine,4-hexanoyltriphenylamine 4- lauroyltriphenylamine,4-hexyltriphenylamine, 4-

dodecyltriphenylamine, 4,4-bis(diphenylamino)benzil,4,4-bis(diphenylamino)benzophenone and the like, and (b) polymerictriarylamines such as 'poly[N,4- '-(N,N' ,N-triphenylbenzidinepolyaidpyltriphenylamine, polysebacyltriphenylamine,polydecamethylenetriphenylamine, poly-n-(4-vinylphenyl)diphenylamine,poly-N-(vinylphenyl)-a,a'- dinaphthylamine andthe like. Other usefulamine-type photoconductors are disclosed in U.S. Pat. No.3,180,730issued Apr. 27, 1965.

Useful photoconductive substances capable of being sensitized inaccordance with this invention are disclosed in Fox U.S. Pat. No.3,265,496 issued Aug. 9, 1966 and include those represented by thefollowing general formula:

R|:III-T Q wherein T represents a mononuclear or polynuclear divalentaromatic radical, either fused or linear (e.g., phenyl, naphthyl,biphenyl, biriaphthyl, etc.), ora substituted divalent aromatic radicalof these types wherein said substituent can comprise a member such as anacyl group having from one to about six carbon atoms (.e.g, acetyl,propionyl, butyryl, etc.), an alkyl group having from one to aboutsixcarbon atoms (e.g., methyl, ethyl, propyl, butyl, etc), an alkoxygroup having from one to about six carbon atoms (e.g., methoxy, ethoxy,propoxy, pentoxy, etc.), or a'nitro group; M represents a mononuclear orpolynuclear monovalent aromatic radical, either fused or linear (e.g.,phenyl, naphthyl, biphenyl, etc), or a substituted monovalent aromaticradical wherein said substituent can comprise a member, such as an acylgroup having from one to about six carbon atoms (e. g., acetyl,propionyl, butyryl, etc.), an alkyl group having from one to about sixcarbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy grouphaving from one to about six carbon atoms (e.g., methoxy, propoxy,pentoxy, etc.), or a nitro group; O can represent a hydrogen atom, ahalogen atom or an aromatic amino group, such as MNH-; b represents aninteger from 1 to about 12; and, R represents a hydrogen atom, amononuclear or polynuclear aromatic radical, either fused or linear(e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radicalwherein said substituent comprises an alkyl group, an alkoxy group, anacyl group, or a nitro group, or a poly(4-vinylphenyl) group which isbonded to the nitrogenatom by a carbonatom of the phenyl group.

Polyarylalkane photoconductors are particuarly useful in producing thepresent invention. Such photoconductors are described in US. Pat. No.3,274,000, French Pat. No. 1,383,461 and in copending application ofSeus and Goldman titled Photoconductive Element Containing OrganicPhotoconductors Ser. No. 627,857, filed Apr. 3, 1967, now US. Pat No.3,542,544. These photoconductors include leuco bases of diaryl ortriaryl methane dye salts, 1,1,1- triarylalkanes wherein the alkanemoiety has at-least two carbon atoms and tetraarylmethanes, there beingsubstituted an amine group on at least one of the aryl groups attachedto the alkane and methine moieties of the latter two classes ofphotoconductors which are non-leuco base materials.

Preferred polyarylalkane photoconductors can be represented by theformula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, analkyl group, or an aryl group, at least one of D, E and G containing anamino substituent. The aryl groups attached to the central carbon atomare preferably phenyl groups, although naphthyl groups can also be used.Such aryl groups can contain such substituents as alkyl and alkoxytypically having one to eight carbon atoms, hydroxy, halogen, etc., inthe ortho, meta or para positions, ortho-substituted phenyl beingpreferred. The aryl groups can also be joined together or cyclized toform a fluorene moiety, for example. The amino substituent can berepresented by the formula wherein each L can be alkyl group typicallyhaving one to eight carbon atoms, a hydrogen atom, an aryl group,

or together the necessary atoms to form a heterocyclic' amino grouptypically having five to six atoms in the ring such as morpholino,pyridyl, pyrryl, etc. At least one of D, E and G is preferablyp-dialkylam'inophenyl group. When J is an alkyl group, such an alkylgroup more generally has one to seven carbon toms.

Representative useful polyarylalkane photoconductors include thecompounds listed in Table 11.

TABLE II Compound Number Name of Compound 14,4'-benzylidenebis(N,N-diethyl-m-toluidine) 24,4"-diamino-4-dimethylamino-2',

,2"-dimethyltriphenylmethane Y 34',4"-bis(diethylamino)-2,6-dichloro2',2"-

. dimethyltriphenylmethane 4 4',4"bis(diethylamino)-2',2"-dimethyldiphenylnaphthylmethane 52',2"-dimethyl-4,4,4"-tris(dimethylamino)- triphenylmethane 64,4"-bis(diethylamino)-4-dimethylamino- 2',2"-dimethyltriphenylmethane 74',4"-bis(diethylamin0)-2-chloro-2,2"-

dimethyl-4-dimethylaminotriphenylmethane 84',4"-bis(diethylamino)-4-dimethylamino-2,2',2"-trimethyltriphenylmethane 94',4"-bis(dimethylamino)-2-chloro-2,2"-

dimethyltriphenylmethane 4,4"-bis(dimethylamino)-2,2"-dimethyl-4-methoxytriphenylmethane bis( 4-diethylamino l l l -tripl1enylethanebis(4-diethylamino)tetraphenylmethane 4',4"-bis(benzylethylamino)-2',2"-dimethyltriphenylmethane4',4"-bis(diethylamino)-2',2"-diethoxytriphenylmethane4,4-bis(dimethylamino)-1.1,l-triphenyleth ne- .7 a;1-(4N,N-dimethylaminophenyT 1 1 diphenylethane4-dimethylaminotetraphenylmethane 4-diethylaminotetraphenylmethanewherein R, and R are each phenyl radicals including substitued phenylradicals and particularly when R, is a phenyl radical havingthe'formula:

lam

wherein R and R are each aryl radicals, aliphatic residues of one to 12carbon atoms such as alkyl radicals preferably having one to four carbonatoms or hydrogen. Particularly advantageous results. are obtained whenR, is a phenyl" radical including substituted phenyl radicals an where Ris diphenylaminophenyl, dimethylaminophenyl or phenyl.

Representative photoconductive compounds useful with sensitizing amountsof the feature'material of this invention includethe following:

TABLE 3 Compound Number Name of Compound 14',4"-bis(diethylamino)-2',2"-dimethyltriphenylmethane 24',4"-diamino-4-dimethylamino-Z,2",5',5"-

tetramethyltriphenylmethane 3 4',4' '-bis(diethylamino)-2,6-dichloro-2,2"-

dimethyltriphenylmethane 4 4',4"-bis(diethylamino)-2,2"-climethyldi'phenylnaphthylmethane 5 2,2"-dimethyl-4,4,4"-tris(dimethylamino)-triphenylmethane 6 4',4"-bis(diethylamino)-2-dimethy1amino-2,2",5,5"-tetramethyltriphenylmethane 74,4"-bis(diethylamino)-2-chloror-2',2"-

dimethyl-4-dimethylaminotriphenylmethane 84',4"-bis(diethylamino)-4-dimethylamino-2,2,2"-trimethyltriphenylmethane 94',4"-bis(dimethylamino)2-chloro-2,2"-

dimethyltriphenylmethane 4',4"-bis(dimethylamino)-2,2"-dimethyl-4methoxytriphenylmethane I l 4,4"-bis(benzylethylamino)-2',2"-dimethyltriphenylmethane4',4"-bis(diethylamino)-2', 2",

5 ,5 '-tetramethyltriphenylmethane4',4"-bis(diethylamino)-2',2"-diethoxytriphenylmethane Otherphotoconductors which can be used with the present .l-aggregatecontaining compositions include parachlorosil, benzil,trinitrofluoroenone, tetrafluorene,9-dicyanomethylene-2,4,7-trinitrofluorenone, etc.

The following Table 111 comprises a partial listing'of U.S. patentsdisclosing a wide variety of organic photoconductive compounds andcompositions which are useful in practicing this invention.

TABLE Ill 7 Inventor U.S. Pat. No. Inventor US. Pat. No. Hoegl et all.3,037,861 Cassiers 3,158,475 Sues et :11. 3,041,165 Tomanek 3,161,505Schlesinger 3,066,023 Schlesinger 3,163,530 Bethe 3,072,479 Schlesinger3,163,531 Klupl'el et a1. 3,047,095 Schlesinger 3,163,532 Neugebauer eta1. 3,112,197 Hoegl 3,169,060 Cassiers et a1. 3,133,022 Stumpf 3,174,854Schlesinger 3,144,633 Klupfel et 21. 3,180,729 Noe et a1. 3,122,435Klupfel et-al. 3,180,730 Sues et al. 3,127,266 Neugebauer 3,189,447Schlesinger 3,130,046 Neugebauer 3,206,306 Cassiers 3,131,060 Fox3,240,597 Schlesinger 3.139,338 Schlesinger 3,257,202 Schlesinger3,139,339 Sues et al. 3,257,203 Cassiers 3,140,946 Sues et al. 3,257,204Davis et a1. 3,141,770 Fo'x 3,265,496 Ghys 3,148,982 Kosche 3,265,497Cassiers 3,155,503 Noe et al. 3,274,000

The amount of sensitizing dye that is used in conjunction with aphotoconductive layer in accordance with the invention can vary widely.Th optimum concentration in any given case will vary with the specificphotoconductor and sensitizing dye used. In general, effective resultscan be obtained where an appropriate sensitizing dye is used in aconcentration range from about 0.0001 to about 30 percent by weightbased on the weight of the film-forming photoconductive coatingcomposition. Preferably, the sensitizing dye is added directly to thephotoconductive composition to be coated in an amount of from about 0.1to about 10 percent by weight of the total coating composition.

Binders for use in preparing the present sensitized photoconductivelayers are film-forming polymeric binder materials having fairlyhigh'dielectric strength which are good electrically insulatingfilm-forming vehicles. Materials of this type comprise styrenebutadienecopolymers; silicone resins; styrene-alkyd resins; silicone-alkydresins; soyaalkyd resins; poly(vinyl chloride); poly(vinylidenechloride); vinylidene chlorideacrylonitrile copolymers; poly(vinylacetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals),such as poly(vinyl butyral); polyacrylic and methacrylic esters, such aspoly(methyl methacrylate), poly(n-butyl methacrylate), poly(isobutylmethacrylate), etc.: polystyrene; nitrated polystyrene; chlorinatedpolyethylene; polyvinyl-m-bromobenzoate-covinyl acetate;polymethylstyrene; isobutylene polymers; polyesters, such aspoly(ethylenealkaryloxyalky-,

lene terephthalate); phenol formaldehyde resins; ketone resins;polyamides; polycarbonates; polythiocarbonates; poly(ethyleneglycal-co-bishydroxyethoxyphenyl propane terephthalate); etc. Methods ofmaking resins of this type have been described in the prior art, forexample, styrene-alkyd resins can be prepared according to the methoddescribed in U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins ofthe type contemplated for use in the photoconductive layers of theinvention are sold under such trade names as Vitel PE-lOl Cymac,Piccopale 100, Saran F-220 and Lexan 145. Other types of binders whichcan be used in the photoconductive layers of the invention include suchmaterials as paraffin, mineral waxes, etc.

Solvents of choice for preparing coating compositions of the presentinvention can include a number of solvents such as benzene, toluene,acetone, 2- butanone, chlorinated hydrocarbons, e.g., methylenechloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran, ormixtures of these solvents, etc.

In preparing the coating composition useful results are obtained wherethe photoconductor substance is present in an amount equal to at leastabout lweight percent of the coating composition. The upper limit in theamount of photoconductor substance present can be widely varied inaccordance with usual practice. It is usual practice that thephotoconductor substance be present in an amount from about 1 weightpercent of the coating composition to about 99 weight percent of thecoating composition. A preferred weight range for the photoconductorsubstance in the coating composition is from about 10 weight percent toabout 60 weight percent.

Coating thicknesses of the photoconductive composition on a support canvary widely. Normally, a coating in the range of about 10 microns toabout 250 microns before drying is useful for the practice of thisinvention. The preferred range of coating thickness is formed to be inthe range from about 25 microns to about microns before drying althoughuseful results can be obtained outside of this range. As previouslymentioned, more than one layer may be coated on the support. Goodresults are obtainable when a first layer containing a photoconductor, abinder and a sensitizer is overcoated with a second layer of acomposition containing a photoconductor and a binder. The photoconductorand binderemployed in the overcoat can be different than thoseemployed'in the first layer.

Suitable supporting materials for coating the photoconductive layers ofthe present invention can include any of a wide variety of electricallyconducting supports, for example, paper (at a relativev humidity above20 percent); aluminum foil-paper laminates; metal foils such as aluminumfoil, zinc foil, etc; metal plates, such as aluminum, copper, zinc,brass and galvanized plates; vapor deposited metal layers such asnickel, silver, aluminum and the like. An especially useful conducting13 support can be prepared by coating a support material such aspoly(ethylene terephthalate) with a layer containing a semiconductordispersed in a resin. Such conducting layers both with and withoutinsulating barrier layers are described in U.S. Pat. No. 3,245,833.Likewise, a suitable conducting coating can be prepared from the sodiumsalt of a carboxyester lactone of maleic anhydride and a vinyl acetatepolymer. Such kinds of conducting layers and methods for their'optimumpreparation and use are disclosed in U.S. Pats. Nos. 3,007,901 and3,267,807.

Whether a transparent, translucent or opaque supportmaterial is usedwill be determined by the method of exposure to be employed, e.g.,exposure by reflex or by transmission through the original, and by theend use desired of the reproduction. Exposure by reflex, for example,requires that the support transmit light while no such requirement isnecessary for exposures by projection. Similarly transparent supportsare required if the reproduction is to be used for projection purposes;translucent supports are preferred for reflex prints; and opaquesupports are adequate if the image is subsequently transferred by anymeans to another support, the reproduction is satisfactory as obtained,or the reproduction is to be used as a printing plate for preparingmultiple copies of the original.

As used herein and in the appended claims, the terms insulating" andelectrically conductive have reference to materials the surfaceresistivities of which are greater than ohms per square unit (e.g., persquare foot) and less than 10' ohms per square unit (e.g., per squarefoot) respectively.

Electrophotographic elements sensitized in accordance with the presentinvention can be employed in any of the well-known electrophotographicprocesses which require photoconductive layers. One such process is thexerographic process. In a process of this type, an electrophotographicelement is given a blanket electrostatic charge by placing the sameunder a corona discharge device maintained at a potential of from6,000-7,000 volts. This device gives a uniform charge to. the surface ofthe photoconductive layer which charge is retained by the layer becauseof the substantial insulating property of the layer, i.e., the lowconductivity of the layer in the dark. The electrostatic charge formedon the surface of the photoconducting layer is then selectivelydissipated from the surface of the layer by exposure to light through animage-bearing transparency by a conventional exposure operation such as,for example, by contact-printing technique, or by lens projection of animage, etc., to form a latent image in the photoconducting layer. Ofcourse, the exposure can also be a reflex exposure. By exposure of thesurface in any such manner, a charged pattern is created by virtue ofthe fact that light causes the charge to be conducted away in proportionto the amount of the exposure in a particular area. The charge patternremaining after exposure is then developed, i.e., rendered visible, bytreatment with a medium comprising tents, for example, as U.S. Pat. No.2,907,674 and in Australian Pat. No. 212,315. In processes ofelectrophotographic reproduction such as xerography, by selecting adeveloping particle which has as one of its components, a low-meltingresin, it is possible to treat the developed photoconductive materialwith heat and cause the powder to adhere permanently to the surface ofthe photoconductive layer. In other cases, a transfer of the imageformed on the photoconductive layer can be made to a second support,which would then become the final print. Techniques of the typeindicated are well knownin the art and have been described in a numberof U.S. and foreign patents, such as U.S. Pats. Nos. 2,297,691 and2,551,582 and in RCA Review, vol. 15 (1954), pages 469-484.

The following examples are included for af urther understanding of theinvention.

Example 1 An organic electrically insulating photoconductive compositionis prepared from 50 ml of a 10 percent solution of a polycarbonatebinder dissolved in methylene bis(4hydroxyphenyl)-propane (e.g., Lexan145, Genelectrostatically attractable particles having optical eralElectric Co.). Next, 0.05 g. of anhydro-S ,5, 6,6-tetrachloro-l ,l'-diethyl -3,3 -di(3-sulfobutyl)benzimidazolocarbocyanine hydroxide isadded to 3 ml. of methyl alcohol and the mixture is agitated in anultrasonic mixing apparatus to disperse the dye as a colloidalsuspension in the alcohol. This colloidal suspension is then added withstirring to the photoconductive mixture previously prepared. Thecombined mixture is then wet coated at a thickness of microns onto apoly(ethylene terephthalate) film support carrying a conductive layer ofthe sodium salt of a polymeric lactone as described in U.S. Pat. No.3,260,706, The resultant electrophotographic element is then negativelycharged under a corona source and exposed for 1 second using a Bauschand Lomb wedge spectrograph at a slit width of 3 mm. After exposure, theelectrostatic latent image is developed to a visible'image by cascadingover the element a dry developer of the type dc scribed in U.S. ReissuePat. No. 25,136. The resultant wedge spectrogram shows a spectralsensitivity extending from 400 to 630 nm. with a large prominent peakExample 2 The procedure of Example 1 is repeated using triphenylamine asthe photoconductor. Similar results are obtained with thesensitivity ofthe photoconductive e l ement extending well beyond that of the dye inthe nonaggregate state. i

Example 3 A photoconductive composition is prepared from 200 ml. ofmethylene chloride, l8 g. of the binder of Example 1 and 12 g. of thephotoconductor of Example 1. Additional methylene chloride is then addedto the mixture to bring the total weight of the solution to 300 g. Next,0.05 g. of the sensitizing dye of Example 1 is added to 1.5 ml. ofmethyl alcohol. A 10 percent methyl alcohol solution ofp-toluenesulfonic acid is then added dropwise to the dye-alcohol mixturewith stirring and heating until the dye completely dissolves and becomescolorless due to protonation. The colorless solution of protonated dyeis then added to the previously prepared photoconductive composition.After slight mixing of the two solutions, the basic photoconductivecomposition converts the protonated, colorless dye to the colored formand at the same time induces the formation of dye in the J-aggregatestate. After 2 minutes of mixing, the combined materials are coated at a100 microns wet-thickness on the conducting support of Example 1. Theresultant electrophotographic element is then negatively charged under acorona source and a wedge spectrogram is made as described in Example 1with an exposure time of l/ 10 of a second. The spectral response ofthis electrophotographic element extends from 400 to 610 nm. with a peakbetween 560 and 600 nm.

Example 4 An electrophotographic element similar to that in Example 3 isprepared using the following sensitizing dye: anhydro-5,5',6,6-tetrachloro-l l ',3-triethyl-3(3-sulfobutyl)-benzimidazolocarbocyanine hydroxide. A wedge spectrogram ismade on this element in accordance with the previous examples. Thesensitized photoconductive composition shows a spectral sensitivity from400 to 620 nm. with a strong band at 560 to 610 nm. This elementrequires only 1/100 ofa second exposure on the wedge spectrograph torecord a good visible image.

Example 5 An electrophotographic element is prepared in accordance withExample 1 using as the sensitizing dye 3 ,3 '-dimethyl-9-phenyl-4,4',5,5 -dibenzothiacarbocyanine bromide. Wedge spectrograms are made inaccordance with the previous examples. The spectral sensitivity of thesensitized photoconductive composition extends from 500 to about 680 nm.with a peak at.

about 670 nm.

EXAMPLE 6 A 0.1 percent solution of anhydro-5,5',6,6'- tetrachloro-1,1'-diethyl-3 ,3 '-di( 3-sulfobutyl) benzimidazolocarbocyanine hydroxidein an 80/20 ethyl alcohol-water mixture is prepared. Ten ml. of awatersolution of an interpolymer of methyl vinyl ether and maleicanhydride (Gantrez AN-l 19 of General Aniline and Film Corporation) isadded to 2 ml. of the dye solution and the mixture is coated at 100microns wet thickness on a conducting support as in Example 1. The layeris dried and overcoated with a 100 microns wet thickness coating of a 10percent methylene chloride solution of the binderpoly[ethyleneglycol-co-bis- (hydroxyethoxyphenyl)propane terephthalate](Vitel 101 of Goodyear Tire and Rubber Co.) containing 0.3 g of thephotoconductor of Example 1. The overcoat is dried and the resultantelectrophotographic element is charged under a corona chargingapparatus. The double layer element is then exposed for 5 seconds atslit width 5 mm. in a wedge spectrograph as in Example 1, followed bydevelopment using toner of Example 1. The resultant wedge spectrogramshowed a spectral sensitivity extending from 480 to 600 nm. with a peakat 580 nm.

Example 7 A photoconductive composition is prepared containing 18 g ofthe binder of Example 1, 12 g. of the photoconductor of Example 1 in 200ml. of methylene chloride with additional methylene chloride added toadjust the total weight to 300 g. Next, 0.025 g. of the dyeanhydro-5,5,6,6'-tetrachloro-l ,1 ,3-triethyl-3 3-sulfobutyl)benzimidazolocarbocyanine hydroxide is dissolved in 0.5 ml.of a 10 percent methanolic solution of p-toluenesulfonic acid and theresultant dye solution is added to 25 ml. of the previously preparedphotoconductor-containing solution. The combined solutions are thencoated at 100 microns wet-thickness on the conductive support of Example1 to form a control element. After drying the resultantelectrophotographic element is corona charged and exposed for 10 secondsat 10 mm. slit width in a Bausch and Lomb Wedge Spectrograph. Afterexposure, the electrostatic latent image on the control element wasdeveloped with the developer of Example 1. The spectral sensitivity ofthis element extends from 440 to 560 nm. with a very slight peak at 580nm. Next, a coating formulation is prepared as above with the additionof 0.02 g. of poly(vinylbenzyltrimethylammonium chloride) to 25 ml. ofthe above mixture. This combined formulation is coated on a conductivesupport as previously described, exposed in the spectrograph anddeveloped. A high-contrast wedge spectrogram results with only a l/ 10of a second exposure and exhibits a spectral sensitivity from 440 to 620nm. with a large prominent peak at 580 nm., characteristic of the dye inthe J-aggregate state. The spectrophotometric absorption curves of thetwo elements show an approximate 50 percent higher conversion of the dyeto the J-aggregate state in the second coating as compared to thecontrol coating.

Example 8 latent electrostrostatic image is developed as in the previousexamples. The wedge spectrogram which is obtained shows good imagedefination and exhibits a spectral sensitivity having a strong peak at 5nm.

Example 9 The procedure of Example 8 is repeated with the exception ofthe binder used in the photoconductive composition is the binder. ofExample 6. After coating on the specially prepared paper, J-aggregationof the dye occurs on dry down and a wedge spectrogram produced as in thepreceding examples shows a strong peak at 580 nm.

Example 10 A composition is prepared using 0.025 g. of the dyeanhydro-l-ethyl-I-sulfohutyl-2.2'-cyaninc hydroxide in 2.5 ml. of thebinder, photoconductor combination o fEx ample l The sensitizedphotoconductive composition is then coated on the specially preparedsupport of Example 7 dried, charged, exposed and developed-as thepreceding examples. Theresultant wedge spectrogram shows goodelectrophotographic response from 460 to 600 nm. with a definite narrowJ-band response at 580 nm. with an exposure of 1/10 of asecond at mm. Asecond electrophotographic element containing structurally similar dye l,1 -diethyl-2,2-cyanine chloride in place of the previous dye whenexposed for 30. seconds on the-wedge spectrograph exhibits only faintelectrophotographicresponse and shows a peak at 530 nm. with no J -bandresponse. Thisindicates the necessity for the acidic portion of the dyewhen used in conjunction with a basic polymeric substrate or addenda.

Example I l The procedure of Example 4 is repeated using the dye 5,5,6,6'-tetrachloro-l ,-l 3,3 '-tetraethylbenzimidaiolocarbocyaninechloride. The resultant electrophotographic element exhibits J-aggregatespectral sensitivity at 580 nm. Similar results are obtained with anelectrophotographic element prepared as in'Example 4 only usingsulfobutyl)benzimidazolocarbocyanine hydroxide.

Example 12 Two electrophotographic elements areprepared by the procedureof Example 4 using a lzlmixture of the dye of that example with one ofthe following dyes: anhydro-S ,6-dichlorol -ethyl-l ,3 ,3,-trimethyl-'3- -sulrobur 1beitziihiaaiaiaifizfisaaisaeyaame "hydroxideand 5 ,6-dichlorol -B-diethylaminoethyl-3 ,3diethylbenzimidazolothiacarbocyanine iodide. When one of the above dyesis blended withthe dye of Example 4, the spectral sensitivity is shiftedto a shorter wavelength. The above dyemixtures when combined in theelectrophotographic element of Example 4 procedure a broad sensitivitybandwith a shifted maximum response. Using this techniqueof mixingdyes,the spectral sensitivity of a photoconductive compositioncan becontrolled or shifted to a desiredportion of the spectrum.

Example 1 3 A photoconductive composition is prepared by mixing thefollowing ingredients: Binder of Example 6 10.5 g.

Triphenylamine (photoconductor) 3.5

3'-ethyl-l-methyl-5,6'-dinitro-2 phenyl- 3-indolothia- 55 carbo cyaninep-toluenesulfonate 0.14

Methylene chloride 81.9 ml. This composition is coated'onto a conductingsupport as in Example 1 with a coating.blocktemperature of about 50C.After the coating dries the resultant electrophotographic element istested for: spectral sensitivity as in Example 1. Thiscontrolelementzhas a radia-- potential, V0,.to some lower potential, V,whose exact.

resultant electrophotographic' element is, then measured'for spectralsensitivity and found'to have a radiation absorption maximum of 570 nm.

Example 14 Two compositions are prepared using 14 g. of the binder ofExample 6, 0.28 g. of the dye of Example 13 and 81.9 ml. ofmethylene'chloride in each of the compositions. After mixing, each ofthe compositions is 0 coated at a microns wet thickness onto atransparent conductive support as in Example 1. One of these coatings issubjected to fuming with methylene chloride Avhich results in aggregateformation. The control coating (unfumed) and the treated coating arethen measured for spectral sensitivity and found to have radiationabsorption 'maxima at 510 and 560 mm., respectively. The two elementsare then measured for positive and negative electrical speeds asfollows. Each element is electrostatically charged .under a coronasource until the surface potential, as measured by an electrometerprobe, reaches about 600 volts. The charged elements are then exposed toa 3,000K tungsten light source through a stepped density gray scale. Theexposure causes reduction of the surface potential of the elements undereach step of the gray scale from its initial value depends on the actualamount of exposure received by the area. The results of thesemeasurements are then plotted on-a graph of surface potential V vs logexposure for each step. The actual positive or negative speed of thephotoconductive composition used can then be expressed in terms of thereciprocal of the exposure required to reduce the surface potential toany fixed arbitrarily selected value. The actual positive and negativespeed is the numerical expression of 10 divided by the exposure inm'eter-candle-seconds required to reduce the 600v volt surface potentialto a value of 500 volts (100 volt shoulder speed). The positive andnegative 100 volt shoulder speeds of the control coatingare 0 and 0,respectively. The positive and negative 100 volt shoulder speeds of theaggregated coating are 25 and 110, respectively, thus demonstrating thephotoconductive response obtainable from the aggregated dye above.

Example 15 A composition is prepared by dissolving 1.5 g. of the binderof Example 1, 1.0 g. of the photoconductor of Example 1, 50mg. of thedye 2-(5,5'-dicyano-2,4- pentenylidene)-3-ethylbenaothiazoline in 12 cc.of dichloromethane. This solution is coated at a wet thickness ofmicrons on a conductingpaper support in contact with a metal block heldat 15c. The dry coating is then fumed with toluene vapors for -l5minutes during which time it changes from orange to blue violet incolor. The resultant element is positively charged, exposed in a wedgespectrograph and developed as in Example 1. A similar element isprepared without fumabove. The spectral sensitivity of the fumedcoatings extends from 400 to 720 nm; whereas, the non-fumed coating hasessentially no xerographic sensitivity and absorbs essentially no lightof wavelengths longer than Example l6v The four spectral,sensitizing'dyes listed in Table I ing and is then charged, exposed anddeveloped as below are each characterized by their ability to formJ-aggregates in light-sensitive silver halide compositions. Forcomparative purposes, the typical absorption peak of the non-aggregatedform of each dye is also 3-ethylbenzothiazoline Samples of each dye aredissolved in methanol to form dye solutions of three concentrations: afirst concentration corresponding to that typically used to sensitize asilver halide emulsion; a second, higher, concentration corresponding tothat typically used to sensitize an organic photoconductive composition;and a third concentration intermediatev to the first and second.

A portion of each dye-methanol solution is added to identical silverhalide test emulsions to produce dyesensitized emulsion dopes which,except for the presence of the different dyes employed, have thefollowing composition:

Silver Halide Test Composition (excluding sensitizer) 1.22 g. silverhalide emulsion containing 1 mole of silver halide and 30 grams of gelper 6l0 grams of the emulsion of l2%% by weight gel mixture of dyesolvent of l5%.by weight saponin mixture of distilled water total weightAnother portion of each dye-methanol solution is added to identicalorganic photoconductive test compositions to produce dye-sensitizedorganic photocond'uctive dopes .which, except for the particular dyeemployed, have the following compoisition:

Organic Photoconductive Test Composition (excluding sensitizer) VitellOlbinder 1.70 g. l 17.90 g. methylene chloride solvent 0.6 g. oftriphenylamine organic photoconductor 20.2 g. total weight Each of theabove dopes is coated on a support and dried. The sensitized coating aretested for the presence of J-aggregation by observing their absorptioncurves to determine whether they exhitit the characteristic, intenseJ-absorption band seen at a longer wavelength than the broad absorptionbandtypical of the non-aggregated form of the dye. Table 11 shows theresults of these tests. The wavelength of peak absorption presented foreach dye in its silver halide and organic photoconductive testcomposition remains substantially unchanged despite the variance inconcentration of dye in the composition. Accordingly, the wavelengthpresented for each dye represents an average value for the three testcompositions in which it is present.

TABLE 1] Silver Halide (AgX) Composition or Organic Photoconduc-Wavelength of As can be seen in Table II, the dye sensitized silverhalide compositions exhibit the characteristic shift in absorption peakindicating that J-aggregation is present. The organic photoconductivecompositions, however, show no such shift in absorption peak indicatingthat the dyes present therein remain in nonaggregated form. The resultsof this example are to be compared with those of Examples 4,5,1'0, and15 above which in accordance with the discovery of the present inventionteach that .l-aggregation of Dyes Nos. l-4 in organic photoconductivecompositions may be obtained. From the above, it is apparent that.I-aggregated dye formation in silver halide emulsions and otherinorganic light sitions. v

Example 17 1.0 g of polyvinyl m-bromobenzoate-co-vinyl acetate binder,1.0g of 4,4-bis(diphenylaminochalcone) organic photoconductor and 0.04 gof 6-chloro-l methyl-l ,2 ,3 -triphenylimdiazo[4,5'-quinoxalino-3'-indolocarbocyanine sensitizing dye is dissolved in15.6 g of methylene chloride by stirring the solids in the solvent for 1hour at room temperature. The resulting solution is hand coated at a wetcoating thickness of 0.004 inch on a conducting layer comprising thesodium salt of a carboxyester lactone which is in turn coated on acellulose acetate film base. After dying, the absorption curve of thesensitized coating is measured and found to exhibit a broad peak at 528nm. Comparison with'the broad 505 nm. absorption peak exhibited by thenonaggregated dye in methanol solution'shows that no J- aggregationoccurs in the organic photoconductive composition. Viewing thesensitized coating under a microscope at 500x magnification furtherindicates that the J-aggregated dye is not present since dye particlesare not observed. This Example shows that simple addition of sensitizingdyes to the above-noted organic chalcone photoconductive compositiondoes not produce J-aggregation of thedye in the above-described organicphotoconductive composition.

Example 18 Example 17 is repeated except that 6,6'-dichloro-1,1'-3,3'-tetraphenylimidazo [4,5-b]- quinoxalinocarbocyaninep-toluenesulfonate is employed as the sensitizer in the organicphotoconductive composition. The coating exhibits a broad absorptionpeak at 618 nm, as compared with the broad peak at 605 nm which th'edyeshows in methanol solution. Viewing at SOOX magnification does notreveal the Presence of p-toluenesulfonate 4. A photoconductivecomposition as in claim 1 wherein the organic photoconductor is selectedfrom the group consisting of a polyarylalkane and an arylamine.

5. An electrophotographic element comprising a conducting support havingcoated thereon an electrically insulating polymer binder material, anorganic photoconductor and a sensitizing amount of at least onesensitizing methine dye which is present in the J- aggregated state andwhich spectrally responds primarily in the region of J-aggregation.

6. An electrophotographic element as in claim wherein the sensitizingmethine dye is selected from the group consisting of cyanine andmerocyanine dyes.

7. An electrophotographic element as in claim 5 wherein the organicphotoconductor is selected from the group consisting of polyarylalkane,arylamine, and 4-diarylamino-substituted chalcone photoconductors.

8. An electrophotographic element comprising a conducting support havingcoated thereon the photoconductive composition of claim 3.

9. A method for producing a sensitizing photoconductive compositioncomprising the steps of combining in solution an organic photoconductor,an electrically insulating polymeric material and a charged form of amethine dye capable of forming J-aggregates, adding an organic polymerhaving a charge of opposite polarity from said dye, mixing thecombination, coating a layer of the combined materials on aconductingsupport and drying the coating to form a heterogeneous coating in whichthe dye present spectrally responds primarily in the region ofJ-aggregation.

10. A method for the sensitization of photoconductors comprising thesteps of protonating a methine dye capable of forming J-aggregates,combining the protonated dye with an electrically insulating polymericmaterial, neutralizing the protonated dye to form a heterogeneouscomposition in which the sensitizng dye present spectrally'respondspredominantly in the region of J-aggregation and adding a sensitizingamount of the resulting heterogeneouscomposition to a photoconductivecomposition comprising an organic photoconductor in a polymerichydrophobic binder.

11. An electrophotographic element comprising an electrically conductivesupport having coated thereon a photoconductive electrically insulatingcomposition comprised of an organic photoconductor, an electricallyinsulating, film-forming polycarbonate resin binder, and a sensitizingamount of at least one cyanine dye capable of forming J-aggregates, saiddye being present in the J-ag'gregated state and said composition beingcharacterized in that it spectrally responds primarily in the region ofJ-aggregation of the dye.

12. An electrophotographic element as in claim 11 wherein theJ-aggregated state of the dye is comprised of particles having a size offrom about 2X10 to about lXlO mm.

13. An electrophotographic element as in claim 12 wherein the dye isanhydro-5,5,6,6'-t etrach1oro-l,1-diethyl-3,3'di(3-sulfobutyl)benzimidazolocarbocyanine hydroxide.

14. An electrophotographic element as in claim 12 wherein the dye is3,3'-dimethyl-9-phenyl-4,4',5,5'- dibenzothiacarbocyanine bromide.

15. An electrophotographic element as in claim 12 wherein the dye isl-ethyl-l '-sulfobutylcyanine hydroxide.

16. An electrophotographic element as in claim 12 wherein the dye is5,5',6,6-tetrachloro-l,1',3,3'- tetraethylbenzimidazolocarbocyaninechloride.

17. An electrophotographic element as in claim 12 wherein the dye is2(-5,5'-dicyano-2,4-pentenylidene)- 3-ethylbenzothiazoline.

3 7 30 UNITED STATES PATENT OFFICE CERTIFICATE. OF CORRECTION 3,769,011Dated October 30, .1973

Patent No. lnventqfls) Paul B. Gilman and Donald w.; H eseltine t errorappears in the above-identified patent It is certified tha herebycorrected as shown below:

' and that said Letters Patent are Column 23, claim 9, first sentence,"sensitizing" should read --sensitized-- Signed and sealed this 1113511day of May 1971+.

(SEAL) Attest: v

EDWARD II.FLETCIER,JR. 1 I c. MARSHALL DANN Atte sting Officer-Commissioner of Patents

2. A photoconductive composition as in claim 1 wherein the sensitizingdye is selected from the group consisting of cyanine, merocyanine andstyryl dyes.
 3. A photoconductive composition as in claim 1 wherein thesensitizing dye is selected from the group consisting of:3,3-diethyl-5,5''-dimethyl-9-ethyl-thiacarbocyanine chloride,anhydro-5,5'',6,6''-tetrachloro-1,1'',3-triethyl-3''-(3-sulfobutyl)benzimidazolocarbocyanine hydroxide,anhydro-1-ethyl-1-(4-sulfobutyl)-2,2''-cyanine hydroxide,3,3''-dimethyl-9-phenyl-4,5 4'',5''-dibenzothiacarbocyanine bromide,anhydro-5,5'',6,6''-tetrachloro-1,1-diethyl-3,3''-di-(3-sulfobutyl)benzimidazolocarbocyanine hydroxide,5,5''-dichloro-1,1'',3,3''-tetramethylbenzimidazolocarbocyanineperchlorate 1'',3-diethylthia-2''-cyanine chloride3,3'',9-triethylselenathiacarbocyanine perchlorate 3,3''-dimethyl-8,10-diphenoxyoxacarbocyanine chloride2-(5,5''-dicyano-2,4-pentenylidene)-3-ethylbenzothiazoline3,3''-diethyl-9-methylthiacarbocyanine chloride1''-ethyl-3-methylthia-2''-cyanine chloride1,1''-diethyl-6,6''-dimethyl-2,2''-cyanine perchlorate3,3'',9-triethyl-5,5''-diphenyloxacarbocyanine hydroxideanhydro-3,9-diethyl-3''-sulfobutyl-5,5''-dichlorothiacarbocyaninebromide 3,3''-dimethyl-9-ethylthiacarbocyanine bromide3,3''-diethyl-9-methyl-4,5,4'',5''-dibenzothiacarbocyanine bromide3,3''-dimethyl-9-phenyl-4,5,4'',5''-dibenzothiacarbocyanine bromide1,1''-diethyl-2,2''-cyanine chloride3''-ethyl-1-methyl-5,6''-dinitro-2-phenyl-3-indolothiacarbocyaninep-toluenesulfonate 2(2-(2-(4-bromophenyl)-6-methoxyimidazo(1,2-b)pyridazin-3-yl)vinyl)-3-ethyl-6-nitrobenzothiazoliump-toluenesulfonateanhydro-2-(2-(3,5-dimethyl-1-p-sulfophenyl-4-pyrozolyl)-vinyl)-3-ethylthiazolo( 4,5-b)quinolinium hydroxide 3''-ethyl-1-methyl-5,6''-dinitro-2-phenyl-3-indolothiacarbocyanine p-toluenesulfonate1,3,3,3'' -tetramethyl-5,6''-dinitroindothiacyanine p-toluenesulfonate2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-ethylthiazolo( 4,5-b)quinolinium chloride 3,3'',9-triethyl-5,5''-diphenyloxacarbocyaninebromide 3,3''-diethyl-9-methylthiacarbocyanine p-toluenesulfonateanhydro-6-chloro-2-(2-(3,5-dimethyl-1-p-sulfophenyl-4-pyrazolyl)vinyl)-1,3-diphenylimidazo(4,5-b)quinoxalinium hydroxide 6,7-dichloro-1'',3'',3''-trimethyl-1,3-diphenylimidazo(4,5-b)-quinoxalinoindocarbocyanineiodide4-p-dimethylaminobenzylidene-3-methyl-1,2,3,4-tetrahydropyrido/2,1-b/benzothiazolium iodide3''-ethyl-1-methyl-5,6''-dinitro-2-phenyl-3-indolothiacarbocyaninep-toluenesulfonate2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-1,3,3-trimethyl-3H-pyRrolo(2,3-b)pyridinium iodide 1,3-diallyl-3''-methyl-6''-nitroimidazo(4,5-b)quinoxalinothiacyanine p-toluenesulfonate3-ethyl-6-nitro-2-(2-(1-phenyl-4-pyrazolyl)vinyl)benzothiazoliump-toluenesulfonate2-(2-(1-(2-benzothiazolyl)3,5-dimethyl-4-pyrazolyl)vinyl)-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate1,3-diallyl-2-(2-(1-phenyl-4-pyrazolyl)vinyl)imidazo(4,5-b)-quinoxalinium p-toluenesulfonateanhydro-2-(2-(3,5-dimethyl-1-p-sulfophenyl-4-pyrazolyl)-vinyl)-3-ethylthiazolo(4,5-b)quinolinium hydroxide6,7-dichloro-2-(2-(1-methyl-2-phenyl-3-indolyl)vinyl)-1,3-diphenylimidazo(4,5-b)quinoxalinium p-toluenesulfonate1,3-diallyl-1''-methyl-5''-nitro-2''-phenylimidazo(4,5-b)-quinoxalino-3''-indolocarbocyanine p-toluenesulfonate3''-ethyl-1,3,3-trimethyl-5,6''-dinitroindothiacarbocyaninep-toluenesulfonate5-chloro-2-(2-(3,5-dimethyl-1-phenyl-4pyrozolyl)vinyl)-1,3,3-trimethyl-3H-indoliumiodide 1,1'',3,3''-tetraethylimidazo( 4,5-b)quinoxalinocarbocyaninechloride 3-((6,7-dichloro-1,3-diphenyl-1H-imidazo(4,5-b)quinoxalin-2(3H)ylidene)ethylidene)-2H-pyrido(1,2-a)pyrimidine-2,4-(3H)-dione5,5''-dichloro-3,3''-diethyl-6,6''-dinitrothiacarbocyanine iodide3-ethyl-6-nitro-2-(2-(1,3,5-triphenyl-4-pyrazolyl)vinyl)-benzothiazoliumiodide2-(2-(2-(4-bromophenyl)-6-methoxyimidazo(1,2-b)pyridazin-3-yl)vinyl)-3-ethyl-6-nitrobenzothiazoliump-toluene-sulfonate2-(2-(2-(4-bromophenyl)-6-methoxyimidazo(1,2-b)pyridazin-3-yl)vinyl)-1,3,3-trimethyl-5-nitro-3H-indolium p-toluenesulfonate3''-ethyl-6,6''-dinitro-1,3-diphenylimidazo(4,5-b)quinoxalinothiacarbocyanine p-toluenesulfonate1,3-diallyl-6''-nitro-1'',3''-diphenylimidazo(4,5-b)quinoxalinocarbocyanine p-toluenesulfonate1,3,3''-triethylimidazo( 4,5-b)quinoxalinothiacarbocyanine iodide2-p-diethylaminostyryl-3-ethyl-6-(2-oxo-1-pyrrolidinyl) benzothiazolium.4. A photoconductive composition as in claim 1 wherein the organicphotoconductor is selected from the group consisting of a polyarylalkaneand an arylamine.
 5. An electrophotographic element comprising aconducting support having coated thereon an electrically insulatingpolymer binder material, an organic photoconductor and a sensitizingamount of at least one sensitizing methine dye which is present in theJ-aggregated state and which spectrally responds primarily in the regionof J-aggregation.
 6. An electrophotographic element as in claim 5wherein the sensitizing methine dye is selected from the groupconsisting of cyanine and merocyanine dyes.
 7. An electrophotographicelement as in claim 5 wherein the organic photoconductor is selectedfrom the group consisting of polyarylalkane, arylamine, and4-diarylamino-substituted chalcone photoconductors.
 8. Anelectrophotographic element comprising a conducting support havingcoated thereon the photoconductive composition of claim
 3. 9. A methodfor producing a sensitized photoconductive composition comprising thesteps of combining in solution an organic photoconductor, anelectrically insulating polymeric material and a charged form of amethine dye capable of forming J-aggregates, adding an Organic polymerhaving a charge of opposite polarity from said dye, mixing thecombination, coating a layer of the combined materials on a conductingsupport and drying the coating to form a heterogeneous coating in whichthe dye present spectrally responds primarily in the region ofJ-aggregation.
 10. A method for the sensitization of photoconductorscomprising the steps of protonating a methine dye capable of formingJ-aggregates, combining the protonated dye with an electricallyinsulating polymeric material, neutralizing the protonated dye to form aheterogeneous composition in which the sensitizng dye present spectrallyresponds predominantly in the region of J-aggregation and adding asensitizing amount of the resulting heterogeneous composition to aphotoconductive composition comprising an organic photoconductor in apolymeric hydrophobic binder.
 11. An electrophotographic elementcomprising an electrically conductive support having coated thereon aphotoconductive electrically insulating composition comprised of anorganic photoconductor, an electrically insulating, film-formingpolycarbonate resin binder, and a sensitizing amount of at least onecyanine dye capable of forming J-aggregates, said dye being present inthe J-aggregated state and said composition being characterized in thatit spectrally responds primarily in the region of J-aggregation of thedye.
 12. An electrophotographic element as in claim 11 wherein theJ-aggregated state of the dye is comprised of particles having a size offrom about 2 X 10 6 to about 1 X 10 1mm.
 13. An electrophotographicelement as in claim 12 wherein the dye isanhydro-5,5'',6,6''-tetrachloro-1,1''-diethyl-3,3''-di(3-sulfobutyl)benzimidazolocarbocyanine hydroxide.
 14. Anelectrophotographic element as in claim 12 wherein the dye is3,3''-dimethyl-9-phenyl-4,4'',5,5''-dibenzothiacarbocyanine bromide. 15.An electrophotographic element as in claim 12 wherein the dye is1-ethyl-1''-sulfobutylcyanine hydroxide.
 16. An electrophotographicelement as in claim 12 wherein the dye is5,5'',6,6''-tetrachloro-1,1'',3,3'' -tetraethylbenzimidazolocarbocyaninechloride.
 17. An electrophotographic element as in claim 12 wherein thedye is 2(-5,5''-dicyano-2,4-pentenylidene)-3-ethylbenzothiazoline.